Can't properly unwrap a simple mesh
Binary rounding errors are possible if the values used are very small or very large, or have a lot of significant figures. Blender uses 32bit floats to store values, so it is very possible to observe binary rounding errors in Blender in some cases. However I believe this is more likely because of the unwrapping algorythm used(maybe binary rounding errors are more visible when using it - I am not sure). If you try choosing Conformal instead of Angle Based this will probably solve the issue: